Packaging containers for consumer use are provided with an opening device of some sort. Some preferential features of an opening device are that it should be easy to actuate and provide an adequate and reliable seal for the product contained in the packaging container. The definition of an adequate seal will vary, depending on the type of product contained in the packaging container, and how the packaging container will be stored etc. A common demand is that the opening device, before it is opened the first time, should prevent microorganisms from accessing the product from outside, since this will rapidly deteriorate the quality of the product. In some instances it is also desired to prevent certain gases, such as oxygen, from entering the packaging container. Since a regular screw cap typically does not provide an adequate seal, a membrane is typically added. The membrane seals the opening of the packaging container by providing a continuous mass of material which is typically welded to a rim of the opening of the packaging container. In a case where gases should be prevented from entering the packaging container, this usually accomplished by use of suitable barrier materials for the opening device, the membrane, and the packaging container itself.
An opening device comprising a cap and a membrane is e.g. disclosed in WO02/070365.
U.S. Pat. No. 5,413,238 shows a closure unit having a protection/support zone made from a first material and a pouring part made from a second material. A similar device is disclosed in EP0546999.